1. Field of the Invention
The present invention relates generally to temperature sensors, and, in particular, to a thin-film deposited temperature sensor.
2. Description of the Prior Art
The most commonly used resistance thermometer at the present time includes a sensor constructed of a wire coil, the resistance of which changes in a predetermined known manner as a function of temperature. These wire coils have been made of nickel, platinum, tungsten, nicrome (an alloy of nickel and chromium) and other materials having a suitably high temperature coefficient of resistivity (TCR). To achieve the requisite high degree of accuracy with such a wire sensor, the material must have high electrical resistance which, in turn, necessitates the use of a relatively long length of wire of small diameter. The reason for this is a high resistance sensor has correspondingly high change of resistance for a change of temperature, and, therefore, is more easily calibrated than a low resistance sensor would be. In addition, a wire coil can only be loosely supported on an insulating substrate and must be annealed in order to obtain a predictable and repeatable resistance. All of these requirements result in the wire coil being relatively fragile and susceptible to breakage from vibrations, shock, and, as well, contamination from external materials.
On the other hand, thin-film temperature sensors can be constructed having very high resistance and at the same time be exceptionally rugged and not readily damaged by normally occurring external circumstances. In addition, thin-film temperature sensors may be deposited on very small substrates providing an improved advantage with respect to size, weight and response time over coil sensors. Still further, shocks and vibrations do not affect deposited film resistors since the substrate is relatively rigid and the resistor may be coated, making it substantially immune to contamination from the outside.